Polyester resin and optical lens

ABSTRACT

A polyester resin having a diol unit containing a unit derived from ethylene glycol and a unit derived from a diol represented by the following formula (I), and a dicarboxylic acid unit containing a unit derived from an aromatic dicarboxylic acid in an amount of 50 mol % or more; wherein the entire diol unit contains the unit derived from ethylene glycol in an amount of 40 to 99 mol %, and the unit derived from a diol represented by formula (I) in an amount of 1 to 60 mol %: 
     
       
         
         
             
             
         
       
     
     wherein A represents an aromatic ring selected from the group consisting of benzene, naphthalene, anthracene, phenanthrene and pyrene; R 1  represents a C1 to C12 alkyl group, a substituted or unsubstituted C6 to C12 aryl group or a halogen atom; n represents an integer of 0 to 4; and when plural R 1 s are present, R 1 s may be the same as or different from each other.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of pending U.S. patentapplication Ser. No. 13/519,694, which is a National Phase ofPCT/JP2010/073372 filed Dec. 24, 2010 and claims the benefit of JapaneseApplication No. 2010-002071 filed Jan. 7, 2010. The disclosures of U.S.patent application Ser. No. 13/519,694 and PCT/JP2010/073372 areincorporated by reference herein their entireties.

TECHNICAL FIELD

The present invention relates to a polyester resin and to an opticallens. More particularly, the present invention relates to a polyesterresin which is suitable for use as a material for an optical lens, andto an optical lens produced through molding of the resin.

BACKGROUND ART

Polyethylene terephthalate (PET) is a thermoplastic resin which isuseful as a material for producing various molded products. Meanwhile,polyethylene naphthalate (PEN) exhibits excellent fundamental propertiessuch as heat resistance, gas barrier property, and chemical resistance,as compared with PET. These thermoplastic polyester resins are widelyused in a variety of applications including bottles, sheets and films.

However, PET or PEN exhibits high crystallinity and poses a problem inthat it generates spherocrystal, which may cause turbidity or glare,during melting during the course of, for example, a molding process.Formation of a highly transparent product from PET or PEN is effectivelycarried out through a molding process in which crystallization israpidly completed by performing crystallization during stretchingwithout involving generation of spherocrystal. Thus, application of PETor PEN is limited to thin products such as bottles, films and sheets,which involve stretching when being formed; i.e., PET or PEN has not yetbeen widely applied to thick molded products.

As has been widely known, the crystallinity of a resin can beeffectively lowered by copolymerizing or blending the resin with a thirdcomponent. An amorphous polymer material can be applied to thick moldedproducts without causing turbidity or glare, which would otherwise occurthrough crystallization. Therefore, in the case of production of athermoplastic polyester resin, when the thermoplastic polyester resin iscopolymerized with a monomer forming an amorphous polymer material, orwhen the resin is blended with an amorphous polymer material, thecrystallinity of the resin can be lowered.

However, such a method poses a problem in that the glass transitiontemperature of the thermoplastic polyester resin is lowered throughincorporation of an amorphous polymer material or a monomer thereof, andthus the heat resistance of the resin is impaired.

In general, in optical systems of various types of cameras such as acamera, a one-time-use camera and a video camera, aberration iscorrected by using a plurality of concave lenses and convex lenses incombination. Specifically, chromatic aberration formed by a convex lensis corrected with chromatic aberration formed by a concave lens that isopposite that of the convex lens. In this case, the concave lens foraberration correction is required to exhibit high dispersion (i.e., lowAbbe number). Optical glass or an optical transparent resin is employedas a material for an optical device used in the optical system of such acamera.

Optical glass exhibits excellent heat resistance, transparency,dimensional stability, chemical resistance and the like, and there arevarious optical glass materials having different refractive indexes andAbbe numbers. However, optical glass poses problems in terms of highmaterial cost, poor moldability, and low productivity. Particularly,formation of an aspherical lens used for aberration correction requiresa very sophisticated technique and high cost, which is a criticalproblem in practical use.

In contrast to the aforementioned optical glass, an optical transparentresin, in particular a thermoplastic transparent resin has advantages inthat an optical lens can be mass-produced through injection molding ofthe resin, and also an aspherical lens can be readily produced from theresin. An optical lens produced from such a thermoplastic transparentresin is applied to a lens for a camera. Examples of the thermoplastictransparent resin include polycarbonate formed of bisphenol A,polymethyl methacrylate and amorphous polyolefin.

As for high dispersion (low Abbe number) of the aforementioned opticalthermoplastic resins, polycarbonate formed of bisphenol A has arefractive index of about 1.59 and an Abbe number of about 32;polymethyl methacrylate has a refractive index of about 1.49 and an Abbenumber of about 58; and amorphous polyolefin has a refractive index ofabout 1.54 and an Abbe number of about 56. Of these resins, onlypolycarbonate may be used as a material for producing a lens foraberration correction, but, because of its Abbe number of 32, cannot beconsidered to exhibit sufficiently high dispersion. Therefore, demandhas arisen for a new material which can be used for producing a lens foraberration correction.

Patent Document 1 discloses a polyester resin produced throughcopolymerization of a fluorene dihydroxy compound, which resin has arefractive index of about 1.66 and an Abbe number of about 20, and canbe used for forming a lens for aberration correction. The resindisclosed in Patent Document 1 has a low Abbe number and exhibitssufficiently high dispersion.

CITATION LIST Patent Literature

-   [Patent Document 1] JP-A-2006-335974

SUMMARY OF INVENTION Technical Problem

However, the resin disclosed in Patent Document 1 poses the followingproblems when used for producing an optical lens. Since the resin isformed through copolymerization of a large amount of a fluorenedihydroxy compound, which is bulky and rigid, the resin exhibits veryhigh melt viscosity and thus poor moldability. In order to improve themoldability of the resin, the melt viscosity thereof during molding maybe reduced by elevating the molding temperature or reducing the degreeof polymerization. However, when the molding temperature is elevated,problems may arise in that coloration is likely to occur during molding,and a molding die is contaminated with generated thermal decompositionproducts. Meanwhile, when the degree of polymerization is reduced, thelow-molecular-weight component content of the resin increasesrelatively, whereby the molding die is likely to be contaminated withlow-molecular-weight components or decomposition products thereof.

Thus, there has not yet been disclosed an optical lens formed of athermoplastic resin which exhibits excellent optical properties (highrefractive index and low Abbe number) suitable for forming a lens foraberration correction, and which also exhibits practically sufficientmoldability.

Also, there has not yet been disclosed a polyester material whichexhibits low crystallinity and moldability satisfactory as a moldingmaterial, and which has a glass transition temperature approximatelyequal to that of PET or PEN alone; i.e., heat resistance comparable tothat of PET or PEN alone.

The problem to be solved by the present invention is to provide apolyester resin which exhibits excellent moldability and heatresistance, and has low Abbe number and high refractive index.

Solution to Problem

The present invention provides a polyamide resin and an optical lens, asdescribed below.

[1] A polyester resin comprising:

a diol unit, which contains a unit derived from ethylene glycol and aunit derived from a diol represented by the following formula (I), and

a dicarboxylic acid unit, which contains a unit derived from an aromaticdicarboxylic acid in an amount of 50 mol % or more;

wherein the entire diol unit contains the unit derived from ethyleneglycol in an amount of 40 to 99 mol %, and the unit derived from a dialrepresented by formula (I) in an amount of 1 to 60 mol %:

wherein A represents an aromatic ring selected from the group consistingof benzene, naphthalene, anthracene, phenanthrene and pyrene; R¹represents an alkyl group having to 12 carbon atoms, a substituted orunsubstituted aryl group having 6 to 12 carbon atoms or a halogen atom;n represents an integer of 0 to 4; and when plural R¹s are present, R¹smay be the same as or different from each other.

[2] An optical lens produced through molding of the polyester resinaccording to [1] above.

Advantageous Effects of Invention

The polyester resin of the present invention exhibits low crystallinityand can be formed into a transparent molded product without becomingturbid during molding. The polyester resin has a glass transitiontemperature approximately equal to that of PET or PEN alone; i.e., heatresistance comparable to that of PET or PEN alone. In addition, thepolyester resin exhibits excellent moldability and is injectionmoldable. Also, the polyester resin exhibits high productivity and canbe produced at low cost. The polyester resin of the present inventionhas low Abbe number and high refractive index, and is suitable for useas a material for producing a lens for aberration correction.

DESCRIPTION OF EMBODIMENTS [Polyester Resin]

The polyester resin of the present invention comprises a diol unit,which contains a unit derived from ethylene glycol and a unit derivedfrom a diol represented by the following formula (I), and a dicarboxylicacid unit, which contains a unit derived from an aromatic dicarboxylicacid in an amount of 50 mol % or more:

wherein A represents an aromatic ring selected from the group consistingof benzene, naphthalene, anthracene, phenanthrene and pyrene; R¹represents an alkyl group having 1 to 12 carbon atoms, a substituted orunsubstituted aryl group having 6 to 12 carbon atoms or a halogen atom;n represents an integer of 0 to 4; and when plural R¹s are present, R¹smay be the same as or different from each other.

(Diol Unit)

The diol unit of the polyester resin of the present invention contains aunit derived from ethylene glycol and a unit derived from a diolrepresented by formula (I); and the entire diol unit contains the unitderived from ethylene glycol in an amount of 40 to 99 mol %, and theunit derived from a dial represented by formula (I) in an amount of 1 to60 mol %. When the amount of the unit derived from ethylene glycol fallswithin the aforementioned range, the polyester resin of the presentinvention exhibits favorable heat resistance and optical performance.When the amount of the unit derived from a diol represented by formula(I) falls within the aforementioned range, the polyester resin of thepresent invention exhibits low crystallinity and can be suitablyemployed for producing an optical lens.

In order to improve the heat resistance and optical performance of thepolyester resin, and to reduce the crystallinity thereof, the amount ofthe unit derived from ethylene glycol is preferably 70 to 99 mol %, morepreferably 80 to 90 mol %, further preferably 85 to 90 mol %, on thebasis of the entirety of the diol unit, and the amount of the unitderived from a diol represented by formula (I) is preferably 1 to 30 mol%, more preferably 10 to 20 mol %, further preferably 10 to 15 mol %, onthe basis of the entirety of the diol unit.

Now will be described the diol represented by formula (I).

In formula (I), A represents an aromatic ring selected from the groupconsisting of benzene, naphthalene, anthracene, phenanthrene and pyrene.

In formula (I), R¹ represents an alkyl group having 1 to 12 carbonatoms, a substituted or unsubstituted aryl group having 6 to 10 carbonatoms or a halogen atom.

In the present invention, the alkyl group is a linear, branched orcyclic alkyl group having 1 to 12 carbon atoms, preferably 1 to 9 carbonatoms, more preferably 1 to 4 carbon atoms. Specific examples of thealkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,t-butyl, cyclohexyl and propylcyclohexyl. In the present invention, thearyl group is a substituted or unsubstituted aryl group having 6 to 10carbon atoms, preferably 6 to 8 carbon atoms. Specific examples of thearyl group include phenyl, iodophenyl, dihydroxyphenyl,methoxyhydroxyphenyl and ethoxyhydroxyphenyl. Examples of the halogenatom include fluorine, chlorine, bromine and iodine. R¹ is preferably amethyl group, an isopropyl group, a cyclohexyl group, a phenyl group ora fluorine atom, and particularly preferably a phenyl group, from theviewpoint of the availability of a raw material.

In formula (I), n represents an integer from 0 to 4. When plural R¹s arepresent, R¹s may be the same as or different from each other. From theviewpoint of the availability of a raw material, n is preferably 0 or 1,more preferably 0.

The diol represented by formula (I) is preferably a diol represented byany of the following formulae (Ia) to (Ic). In the following formulae(Ia) to (Ic), R¹ and n have the same meanings as defined above informula (I), and preferred ranges of R¹ and n are the same as thosedescribed above in formula (I).

Specific examples of preferred diols represented by formula (I) include,but are not limited to, 5,5-dimethylol-2-phenyl-1,3-dioxane,5,5-dimethylol-2-(2,4,6-trimethylphenyl)-1,3-dioxane,5,5-dimethylol-2-(3,4-dimethylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-cyclohexylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-isopropylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-fluorophenyl)-1,3-dioxane,5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane,5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane,5,5-dimethylol-2-(2-naphthyl)-1,3-dioxane and5,5-dimethylol-2-(9-anthracenyl)-1,3-dioxane.

Of these, from the viewpoints of optical performance, heat resistance,and economy, preferred are 5,5-dimethylol-2-phenyl-1,3-dioxane,5,5-dimethylol-2-(2,4,6-trimethylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane and5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane, and more preferred are5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane and5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane. These diols may be employedsingly or in combination of two or more species.

No particular limitation is imposed on the method for producing the diolrepresented by formula (I), and the diol may be produced throughreaction between pentaerythritol and an aromatic aldehyde represented bythe following formula (A):

(R¹)_(n)-A-CHO  (A)

wherein A, R¹ and n have the same meanings as defined above in formula(I).

The polyester resin of the present invention may contain a diol unit inaddition to the diol unit containing the unit derived from ethyleneglycol and the unit derived from a diol represented by formula (I), solong as the effects of the invention are not impaired. Specific examplesof the compound which may form such an additional diol unit includealiphatic diols such as trimethylene glycol, 2-methyl-1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol,propylene glycol and neopentyl glycol; alicyclic diols such as2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,3-cyclohexanedimethanol,1,4-cyclohexanedimethanol, 1,2-decahydronaphthalenedimethanol,1,3-decahydronaphthalenedimethanol, 1,4-decahydronaphthalenedimethanol,1,5-decahydronaphthalenedimethanol, 1,6-decahydronaphthalenedimethanol,2,7-decahydronaphthalenedimethanol, tetralindimethanol,norbornanedimethanol, tricyclodecanedimethanol andpentacyclododecanedimethanol; diols having a cyclic acetal skeleton suchas3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecaneand 5-methylol-5-ethyl-2-(1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane; andbisphenol compounds such as 4,4′-isopropylidenediphenol (bisphenol A)and methylenediphenol (bisphenol F). These diols may be employed singlyor in combination of two or more species.

(Dicarboxylic Acid Unit)

The dicarboxylic acid unit of the polyester resin of the presentinvention contains a unit derived from an aromatic dicarboxylic acid inan amount of 50 mol % or more. When the amount of the unit derived froman aromatic dicarboxylic acid falls within the aforementioned range, thepolyester resin of the present invention exhibits favorable heatresistance and optical performance.

In order to improve the heat resistance of the polyester resin, and toachieve high refractive index and low Abbe number thereof, the amount ofthe unit derived from an aromatic dicarboxylic acid is preferably 70 to100 mol %, more preferably 85 to 100 mol %, further preferably 95 to100%, particularly preferably 100 mol %, on the basis of the entirety ofthe dicarboxylic acid unit.

Specific examples of the aromatic dicarboxylic acid include, but are notlimited to, terephthalic acid, isophthalic acid, phthalic acid,2-methylterephthalic acid, naphthalenedicarboxylic acid,biphenyldicarboxylic acid and tetralindicarboxylic acid. Of these,naphthalenedicarboxylic acid is preferred, from the viewpoints ofrefractive index, Abbe number, heat resistance, and economy. Specificexamples of the naphthalenedicarboxylic acid include1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid,1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and2,7-naphthalenedicarboxylic acid. Of these, 2,6-naphthalenedicarboxylicacid is particularly preferred. These aromatic dicarboxylic acids may beemployed singly or in combination of two or more species.

Specific examples of the compound (other than the unit derived from anaromatic dicarboxylic acid) which may form the dicarboxylic acid unitinclude aliphatic dicarboxylic acids such as succinic acid, glutaricacid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacicacid, decanedicarboxylic acid, dodecanedicarboxylic acid,cyclohexanedicarboxylic acid, decalindicarboxylic acid,norbornanedicarboxylic acid, tricyclodecanedicarboxylic acid,pentacyclododecanedicarboxylic acid,3,9-bis(1,1-dimethyl-2-carboxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,5-carboxy-5-ethyl-2-(1,1-dimethyl-2-carboxyethyl)-1,3-dioxane and dimeracid. These compounds may be employed singly or in combination of two ormore species.

(Additional Constitutive Unit)

For the purpose of adjusting melt viscoelasticity, molecular weight,etc., the polyester resin of the present invention may contain amonohydric alcohol unit such as butyl alcohol, hexyl alcohol or octylalcohol; a tri- or more-valent polyhydric alcohol unit such astrimethylolpropane, glycerin, 1,3,5-pentanetriol or pentaerythritol; amonocarboxylic acid unit such as benzoic acid, propionic acid or butyricacid; a polycarboxylic acid unit such as trimellitic acid orpyromellitic acid; or an oxyacid unit such as glycolic acid, lacticacid, hydroxybutyric acid, 2-hydroxyisobutyric acid or hydroxybenzoicacid, so long as the effects of the invention are not impaired.

Since the polyester resin of the present invention is employed forproducing an optical lens, in particular a concave lens for aberrationcorrection, it is preferable that the entire diol unit contains the unitderived from ethylene glycol in an amount of 85 to 90 mol % and the unitderived from a diol represented by formula (I) in an amount of 10 to 15mol %, and that the entire dicarboxylic acid unit contains only a unitderived from 2,6-naphthalenedicarboxylic acid. The polyester resin ofthe present invention having such a composition is well balanced inmoldability, low crystallinity, high heat resistance, high refractiveindex and low Abbe number.

(Production Method for Polyester Resin)

No particular limitation is imposed on the method for producing thepolyester resin of the present invention, and the polyester resin may beproduced through any known method. Specific examples of the method forproducing the polyester resin include melt polymerization methods suchas transesterification and direct esterification; and solutionpolymerization methods. Transesterification is particularly preferred.

Production of the polyester resin may employ, for example, a catalystsuch as a transesterification catalyst, an esterification catalyst or apolycondensation catalyst; a stabilizer such as an etherificationpreventing agent, a thermal stabilizer or a light stabilizer; or apolymerization controlling agent. These may be appropriately selecteddepending on, for example, reaction rate or the color tone, safety,thermal stability, weather resistance or elution property of thepolyester resin.

Specific examples of the catalyst include compounds (e.g., a fatty acidsalt, a carbonic acid salt, a phosphoric acid salt, a hydroxide, achloride, an oxide, and an alkoxide) of metals such as zinc, lead,cerium, cadmium, manganese, cobalt, lithium, sodium, potassium, calcium,nickel, magnesium, vanadium, aluminum, titanium, antimony and tin; andmetallic magnesium. These may be employed singly or in combination oftwo or more species. The transesterification catalyst employed fortransesterification is preferably a manganese compound; specifically,for example, manganese acetate tetrahydrate. The polycondensationcatalyst is preferably an antimony compound; specifically, for example,antimony oxide (III).

The amount of the transesterification catalyst employed fortransesterification is preferably 0.001 to 1 mol %, more preferably0.005 to 0.5 mol %, with respect to the dicarboxylic acid unit. Thepolycondensation catalyst employed is preferably 0.001 to 1 mol %, morepreferably 0.005 to 0.5 mol %, with respect to the dicarboxylic acidunit.

The amount of foreign matter contained in the polyester resin of thepresent invention is preferably reduced to a minimum possible level, inorder to improve the quality of the resin as a product. Therefore, whenthe polyester resin of the present invention is produced, preferably,there are carried out filtration of molten raw materials, filtration ofa catalyst liquid, and filtration of a molten oligomer. The filteremployed for filtration of molten raw materials, a catalyst liquid, or amolten oligomer preferably has a mesh size of 5 μm or less, morepreferably 1 μm or less. Also, the polyester resin produced throughpolymerization is preferably filtered with a polymer filter. The polymerfilter employed preferably has a mesh size of 100 μm or less, morepreferably 30 μm or less. The process for producing resin pellets isdesirably carried out in a low-dust environment, preferably in a class1000 or lower clean room, more preferably in a class 100 or lower cleanroom.

(Polyester Resin Composition)

Optionally, an additive or a molding aid may be added to the polyesterresin of the present invention, to thereby prepare a polyester resincomposition. Examples of the additive and the molding aid include anantioxidant, a light stabilizer, a UV absorbent, a plasticizer, anextender, a matting agent, a drying controlling agent, an antistaticagent, a precipitation preventing agent, a surfactant, a flow-improvingagent, a drying oil, a wax, a filler, a colorant, a reinforcing agent, asurface smoothing agent, a leveling agent, a curing accelerator and athickener. For the purpose of imparting various properties to thepolyester resin of the present invention in consideration of theintended use thereof, the polyester resin may be blended with anadditional resin, to thereby prepare a polyester resin composition.Examples of the additional resin include thermoplastic resins, such aspolyester resin other than the polyester resin of the present invention.

For the purpose of improving moldability, preferably, a flow-improvingagent is added to the polyester resin of the present invention. Theflow-improving agent may be, for example, an ester of a polyfunctionalalcohol and a fatty acid, and is preferably a stearic acid ester ofglycerin. The flow-improving agent content of the polyester resincomposition is preferably 5,000 ppm or less, more preferably 3,000 ppmor less, further preferably 1,000 ppm or less, particularly preferably500 ppm or less, for preventing problems caused by failure in releasingthe composition from a molding die.

(Properties of Polyester Resin)

The polyester resin of the present invention preferably exhibits thefollowing properties (1) to (3):

(1) a midpoint glass transition temperature of 110° C. or higher asmeasured through the plastic transition temperature measuring method inaccordance with JIS K7121;

(2) an intrinsic viscosity (IV) of 0.2 to 1.0 dL/g as measured at 25° C.by use of a solvent mixture of phenol and 1,1,2,2-tetrachloroethane(ratio by mass=6:4); and

(3) a melt mass flow rate of 10 to 200 g/10 min as measured through themelt mass flow rate test method in accordance with JIS K7210 at a testtemperature of 260° C. and a load of 2.16 kgf.

<Property (1): Glass Transition Temperature (Tg)>

As used herein, “glass transition temperature (Tg)” refers to a midpointglass transition temperature (T_(mg)) as measured by means of adifferential scanning calorimeter through the plastic transitiontemperature measuring method in accordance with JIS K7121.

The polyester resin of the present invention preferably has a glasstransition temperature of 110° C. or higher, more preferably 115° C. orhigher, further preferably 120° C. or higher. When the glass transitiontemperature falls within the aforementioned range, an optical lensproduced through molding of the polyester resin of the present inventioncan be subjected to a surface treatment such as hard coating, which ispreferred.

<Property (2): Intrinsic Viscosity (IV)>

The intrinsic viscosity (IV) of the polyester resin of the presentinvention is measured at 25° C. by use of a solvent mixture of phenoland 1,1,2,2-tetrachloroethane (ratio by mass=6:4). The intrinsicviscosity may be measured by means of, for example, an automaticcapillary viscometer (trade name: SS-300-L1, product of ShibayamaScientific Co., Ltd.).

No particular limitation is imposed on the intrinsic viscosity of thepolyester resin of the present invention. However, in order to improvethe moldability and optical performance of the polyester resin, theintrinsic viscosity is preferably 0.3 to 1.2 dL/g, more preferably 0.4to 1.0 dL/g, further preferably 0.5 to 0.8 dL/g.

Since the polyester resin of the present invention is applied to anoptical lens, the intrinsic viscosity thereof is preferably 0.2 to 1.0dL/g, more preferably 0.25 to 0.5 dL/g, further preferably 0.3 to 0.4dL/g. When the intrinsic viscosity falls within this range, occurrenceof birefringence can be prevented during molding; i.e., the polyesterresin is well balanced in moldability and low birefringence.

<Property (3): Melt Mass Flow Rate (MFR)>

The melt mass flow rate (MFR) of the polyester resin of the presentinvention is measured through the melt mass flow rate test method inaccordance with HS K7210 at a test temperature of 260° C. and a load of2.16 kgf. The melt mass flow rate may be measured by means of, forexample, a melt indexer (trade name: C-5059D, product of Toyo SeikiSeisaku-Sho, Ltd.).

No particular limitation is imposed on the melt viscosity of thepolyester resin of the present invention. However, since the polyesterresin is applied to an optical lens, the melt viscosity is preferably 10to 200 g/10 min, more preferably 20 to 150 g/10 min, further preferably30 to 120 g/10 min, particularly preferably 50 to 110 g/10 min. When themelt mass flow rate falls within this range, occurrence of birefringencecan be prevented during molding, and progress of crystallization causedby heat can be prevented during molding; i.e., the polyester resin iswell balanced in moldability, low crystallinity and low birefringence.

<Refractive Index and Abbe Number>

Since the polyester resin of the present invention is employed forproducing an optical lens, in particular a concave lens for aberrationcorrection, the refractive index of the polyester resin is preferably1.59 or more, more preferably 1.61 or more, further preferably 1.63 ormore. No particular limitation is imposed on the maximum refractiveindex, but the refractive index is preferably 1.66 or less, in view ofbalance of the refractive index with other properties.

Since the polyester resin of the present invention is employed forproducing an optical lens, in particular a concave lens for aberrationcorrection, the Abbe number of the polyester resin is preferably 20 orless, more preferably 19 or less. No particular limitation is imposed onthe minimum Abbe number, but the Abbe number is preferably 17 or more,in view of balance of the Abbe number with other properties.

The refractive index and Abbe number of the polyester resin of thepresent invention are measured through the below-described method.Specifically, a right-angled isosceles triangular piece, which has alength of each of the two sides forming the right angle: 20 mm and athickness of 3 mm, is formed through injection molding of the polyesterresin, and the injection-molded piece is subjected to annealing in anoven for 10 hours at a temperature lower by about 20° C. than theaforementioned glass transition temperature of the resin, to therebyprepare a measurement sample. The refractive index and Abbe number ofthe measurement sample are measured at 25° C. The refractive index ismeasured at 589 nm (d line), and the Abbe number is calculated fromrefractive indexes measured at 656 nm (C line), 486 nm (F line), and dline. These values may be measured by means of, for example, an Abberefractometer (trade name: NAR-4T, product of Atago Co., Ltd.).

(Application of Polyester Resin)

The polyester resin of the present invention can be employed for variousapplications. For example, the polyester resin can be employed for, forexample, an injection-molded product and an extrusion-molded product;specifically, a sheet, a film, a pipe, a bottle, a foam product, atackifier, an adhesive, a coating material, and the like. The sheet orthe film may be formed of a single layer or a plurality of layers, andmay be non-stretched or in a monoaxially or biaxially stretched state.Alternatively, the sheet or the film may be stacked on, for example, asteel plate. The bottle may be a direct blow bottle or an injection blowbottle, or may be produced through injection molding. The foam productmay be in the form of foam beads or an extruded foam product.

Particularly, the polyester resin of the present invention can besuitably employed for applications requiring high heat resistance andwater vapor barrier property, including products employed inautomobiles, packaging materials for imports and exports, electronicmaterials such as a back sheet of solar cell, and food packagingmaterials which are subjected to retort treatment or heating with amicrowave oven.

[Optical Lens]

The polyester resin of the present invention can be suitably employedparticularly for producing an optical lens. The optical lens of thepresent invention can be produced through injection molding of thepolyester resin of the present invention by means of an injectionmolding machine or an injection-compression molding machine. When theoptical lens is produced from the polyester resin, in order to reduceincorporation of foreign matter to a minimum possible extent, molding isdesirably carried out in a low-dust environment, preferably in a class1000 or lower clean room, more preferably in a class 100 or lower cleanroom.

The optical lens of the present invention may be a spherical lens or anaspherical lens, but is preferably an aspherical lens. Since sphericalaberration can be substantially nulled by means of a single asphericallens; i.e., a plurality of spherical lenses are not required to beemployed in combination for elimination of spherical aberration, theweight of the optical lens can be reduced, and production cost can bereduced. Among optical lenses, an aspherical lens is particularly usefulas a lens for a camera. Such an aspherical lens preferably has anastigmatism of 0 to 15 ink, more preferably 0 to 10 mλ.

The surface of the optical lens of the present invention may beoptionally provided with, for example, an antireflection layer or ahardcoat layer. The antireflection layer may be formed of a single layeror a plurality of layers. The material of the antireflection layer maybe an organic substance or an inorganic substance, but is preferably aninorganic substance. Specific examples of the inorganic substanceinclude oxides and fluorides, such as silicon oxide, aluminum oxide,zirconium oxide, titanium oxide, cerium oxide, magnesium oxide andmagnesium fluoride.

The optical lens of the present invention can be applied to varioustypes of lenses, including a pick-up lens, an f-θ lens, and a spectaclelens. Since the optical lens of the present invention has highrefractive index and low Abbe number, the optical lens can be suitablyemployed particularly as a lens for chromatic aberration correction.Specifically, the optical lens can be suitably employed as a lens of,for example, a single-lens reflex camera, a digital still camera, avideo camera, a cellular phone with camera, a one-time-use camera, atelescope, binoculars, a microscope, and a projector.

The optical lens of the present invention may be a convex lens or aconcave lens. When, for example, the optical lens of the presentinvention is a concave lens, an optical lens system with reducedchromatic aberration can be formed by combining the concave lens with aconvex lens having a high Abbe number. The Abbe number of the convexlens employed in combination is preferably 40 to 60, more preferably 50to 60.

EXAMPLES

The present invention will next be described in more detail by way ofexamples, which should not be construed as limiting the inventionthereto.

Production Examples 1 and 2 Production of5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane and5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane

N,N-Dimethylacetamide, toluene, pentaerythritol, and p-toluenesulfonicacid dihydrate, in amount of each shown in Table 1, were added to aglass flask, and the resultant mixture was stirred at 100° C.Thereafter, a toluene solution of 1-naphthaldehyde or a toluene solutionof biphenylaldehyde in an amount of shown in Table 1 was added dropwiseto the flask, followed by temperature elevation to 145° C. A distillatecontaining water was separated, and reaction was allowed to proceed forthree to five hours. After completion of reaction, water was added tothe resultant reaction mixture, to thereby precipitate white crystals.Subsequently, filtration, and washing with water were carried out,followed by concentration, to thereby produce5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane or5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane as white crystals.

TABLE 1 Production Production Compound (Unit) Example 1 Example 2N,N-Dimethylacetamide mL 2000 2000 Toluene mL 700 700 Pentaerythritol g100 100 p-Toluenesulfonic acid dihydrate g 20 201-Naphthaldehyde/toluene g/mL 127/700 0 Biphenylaldehyde/toluene g/mL 0134/700 Produced solid NFP MPBP NFP:5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane MPBP:5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane

Examples 1 and 2 Production of Polyester Resin

Raw material monomers in types and amounts of shown in Table 2 wereadded to a glass flask equipped with a heater, a stirring blade, apartial condenser, a trap, a thermometer, and a nitrogen gas feed tube,and the resultant mixture was heated to 215° C. in a nitrogen atmospherein the presence of manganese acetate tetrahydrate in an amount of 0.03mol % with respect to the dicarboxylic acid component, to thereby allowtransesterification reaction to proceed. After the reaction conversionof the dicarboxylic acid component had reached 90% or more, antimonyoxide (III) and triethyl phosphate were added in amounts of 0.02 mol %and 0.06 mol %, respectively, on the basis of 100 mol % of thedicarboxylic acid component, and temperature elevation and pressurereduction were gradually carried out. Finally, polycondensation wascarried out at 250 to 270° C. and 0.1 kPa or less. The reaction wascompleted when an appropriate melt viscosity was achieved, and theresultant polyester resin was recovered.

Comparative Examples 1 and 2 Production of Polyester Resin

Raw material monomers in types and amounts of shown in Table 2 wereadded to a polyester production apparatus equipped with a packing-typerectification column, a partial condenser, a total condenser, a coldtrap, a stirrer, a heater, and a nitrogen gas feed tube, and theresultant mixture was heated to 215° C. in a nitrogen atmosphere in thepresence of manganese acetate tetrahydrate in an amount of 0.03 mol %with respect to the dicarboxylic acid component, to thereby allowtransesterification reaction to proceed. After the reaction conversionof the dicarboxylic acid component had reached 90% or more, antimonyoxide (III) and triethyl phosphate were added in amounts of 0.02 mol %and 0.06 mol %, respectively, on the basis of 100 mol % of thedicarboxylic acid component, and temperature elevation and pressurereduction were gradually carried out. Finally, polycondensation wascarried out at 250 to 270° C. and 0.1 kPa or less. The reaction wascompleted when an appropriate melt viscosity was achieved, and theresultant polyester resin was recovered.

TABLE 2 Compar- Compar- Exam- Exam- ative ative ple 1 ple 2 Example 1Example 2 Dicarboxylic Dimethyl 2,6- 0.949 0.940 218.5 0 acidnaphthalene- component dicarboxylate (mol) Dimethyl 0 0 0 369.5terephthalate Diol NFP 0.095 0 0 0 component MPBP 0 0.094 0 0 (mol)Ethylene glycol 1.613 1.597 393.3 591.2 NFP:5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane MPBP:5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane

(Production of Optical Lens)

The thus-produced polyester resin was dried under vacuum for 10 hours ata temperature lower by 20° C. than the glass transition temperature ofthe resin, and then the resin was subjected to injection molding bymeans of an injection molding machine (trade name: SH50, product ofSumitomo Heavy Industries, Ltd.) at a cylinder temperature of 260° C.and a die temperature lower by 35° C. than the glass transitiontemperature of the resin, to thereby produce a biconvex lens having adiameter of 28 mm and curvature radius in both convex surfaces of 20 mm.

The compositions and properties of the polyester resins produced in theExamples and the Comparative Examples were determined through thebelow-described methods. Also, the lenses produced in the Examples andthe Comparative Examples were evaluated through the below-describedmethod. The results are shown in Table 3.

<Methods for Determining the Composition and Properties of PolyesterResin> (1) Composition of Resin

The proportion of the diol unit and the dicarboxylic acid unit in eachpolyester resin was calculated through ¹H-NMR measurement by means of anNMR apparatus (trade name: JNM-AL400, product of JEOL Ltd.) at 400 MHz.Deuterated chloroform was employed as a solvent.

(2) Glass Transition Temperature (Tg)

The glass transition temperature of each polyester resin was measured bymeans of a differential scanning colorimeter (trade name: DSC/TA-60WS,product of Shimadzu Corporation). Specifically, about 10 mg of thepolyester resin was added to a non-sealed aluminum container, and heatedto 280° C. at a temperature elevation rate of 20° C./min and meltedunder a stream of nitrogen gas (30 mL/min), followed by quenching, tothereby prepare a measurement sample. Measurement was carried out on thethus-prepared sample under the same conditions as described above, andthe midpoint glass transition temperature was calculated in accordancewith JIS K7121.

(3) Intrinsic Viscosity (IV)

The intrinsic viscosity of each polyester resin was measured at 25° C.by means of an automatic capillary viscometer (trade name: SS-300-L1,product of Shibayama Scientific Co., Ltd.). Specifically, 0.5 g of thepolyester resin was heat-dissolved in 120 g of a solvent mixture ofphenol and 1,1,2,2-tetrachloroethane (ratio by mass=6:4), followed byfiltration and then cooling to 25° C., to thereby prepare a measurementsample.

(4) Refractive Index and Abbe Number

The refractive index and Abbe number of each polyester resin weremeasured at 25° C. by means of an Abbe refractometer (trade name:NAR-4T, product of Atago Co., Ltd.). Specifically, the polyester resinwas dried under vacuum for 10 hours at a temperature lower by about 20°C. than the glass transition temperature of the resin, and then theresin was subjected to injection molding by means of an injectionmolding machine (trade name: SH50, product of Sumitomo Heavy Industries,Ltd.) at a cylinder temperature of 280° C. and a die temperature lowerby 20 to 50° C. than the glass transition temperature of the resin, tothereby form a right-angled isosceles triangular piece having a lengthof each of the two sides forming the right angle of 20 mm and athickness of 3 mm. The thus-molded piece was subjected to annealing inan oven for 10 hours at a temperature lower by about 20° C. than theglass transition temperature of the resin, to thereby prepare ameasurement sample. The refractive index was measured at 589 nm (dline), and the Abbe number was calculated from refractive indexesmeasured at 656 nm (C line), 486 nm (F line) and d line.

(5) Melt Mass Flow Rate (MFR)

The melt mass flow rate of each polyester resin was measured by means ofa melt indexer (trade name: C-5059D, product of Toyo Seiki Seisaku-Sho,Ltd.). Specifically, the melt mass flow rate was measured in accordancewith JIS K7210 at a measurement temperature of 260° C. and a load of2.16 kgf.

<Method for Evaluation of Optical Lens> (6) Evaluation of Appearance

The appearance of each optical lens was visually observed, to therebyevaluate in terms of transparency and deformation such as sink orwarpage.

TABLE 3 Compar- Compar- Exam- Exam- ative ative ple 1 ple 2 Example 1Example 2 Composition and properties of polyester resin Copoly- Dimethyl2,6- 100 100 100 0 merization naphthalene- proportions dicarboxylate(mol %) Dimethyl 0 0 0 100 terephthalate NFP 10 0 0 0 MPBP 0 10 0 0Ethylene glycol 90 90 100 100 Glass transition temperature 125 115 12484 (° C.) Intrinsic viscosity (dL/g) 0.32 0.28 0.55 0.72 Refractiveindex 1.647 1.646 1.649 1.575 Abbe number 18.6 18.7 65 39 MFR (g/10 min)116 178 4.8 5.3 Evaluation of optical lens Transparency Good Good TurbidTurbid Deformation Ab- Ab- Presence Presence sence sence NFP:5,5-dimethylol-2-(1-naphthyl)-1,3-dioxane MPBP:5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane

The polyester resin of Comparative Example 1 or 2 (PEN or PET), whichdid not contain a unit derived from a diol represented by formula (I),was found to exhibit high intrinsic viscosity, low melt mass flow rate,poor injection moldability, and high Abbe number. The optical lensproduced through injection molding of the polyester resin of ComparativeExample 1 or 2 exhibited high crystallinity and poor transparency (i.e.,turbidity) and showed deformation by sink or warpage.

In contrast, the polyester resin of Example 1 or 2, which contained adiol unit derived from a diol represented by formula (I), was found toexhibit low intrinsic viscosity, high melt mass flow rate, excellentinjection moldability, low Abbe number, and high refractive index. Thepolyester resin of Example 1 exhibited a glass transition temperaturewhich was approximately equal to that of PEN alone (Comparative Example1). Meanwhile, the polyester resin of Example 2 exhibited a glasstransition temperature which was slightly lower than that of PEN alone(Comparative Example 1), but was considerably higher than that of PETalone (Comparative Example 2). That is, the polyester resins of Examples1 and 2 exhibited excellent heat resistance. Hitherto, when attempts aremade to improve the crystallinity of PET or PEN, problems may arise inthat the glass transition temperature thereof is lowered, and thus theheat resistance thereof is impaired. In contrast, the polyester resin ofthe present invention exhibits low crystallinity and moldabilitysatisfactory as a molding material, and has a glass transitiontemperature approximately equal to that of PET or PEN alone; i.e., heatresistance comparable to that of PET or PEN alone.

The optical lens produced through injection molding of the polyesterresin of Example 1 or 2 exhibited excellent transparency, excellentmoldability, no deformation, low Abbe number, and high refractive index.Therefore, the optical lens exhibited excellent properties as a lens foraberration correction.

INDUSTRIAL APPLICABILITY

The polyester resin of the present invention is suitable for use as amaterial for an optical lens of, for example, a camera, a telescope,binoculars, or a television projector. The polyester resin is veryuseful, since an aspherical lens of high refractive index and lowbirefringence (such a lens is technically difficult to produce fromglass) can be effectively produced through injection molding of thepolyester resin at low cost. Particularly, the polyester resin of thepresent invention can be suitably employed for producing a lens forchromatic aberration correction.

What is claimed is:
 1. A polyester resin comprising: a diol unit, whichcontains a unit derived from ethylene glycol and a unit derived from adiol represented by the following formula (I), and a dicarboxylic acidunit, which contains a unit derived from an aromatic dicarboxylic acidin an amount of 50 mol % or more; wherein the entire diol unit containsthe unit derived from ethylene glycol in an amount of 40 to 99 mol %,and the unit derived from a diol represented by formula (I) in an amountof 1 to 60 mol %:

wherein A represents benzene; R¹ represents an alkyl group having 1 to12 carbon atoms, a substituted or unsubstituted aryl group having 6 to12 carbon atoms or a halogen atom; n represents an integer of 1 to 4;and when plural R¹s are present, R¹s may be the same as or differentfrom each other.
 2. The polyester resin according to claim 1, whereinthe aromatic dicarboxylic acid is a naphthalenedicarboxylic acid.
 3. Thepolyester resin according to claim 2, wherein thenaphthalenedicarboxylic acid is 2,6-naphthalenedicarboxylic acid.
 4. Thepolyester resin according to claim 1, wherein the diol represented byformula (I) is at least one selected from the group consisting of5,5-dimethylol-2-(2,4,6-trimethylphenyl)-1,3-dioxane,5,5-dimethylol-2-(3,4-dimethylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-cyclohexylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-isopropylphenyl)-1,3-dioxane,5,5-dimethylol-2-(4-fluorophenyl)-1,3-dioxane, and5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane.
 5. The polyester resinaccording to claim 4, wherein the diol represented by formula (I) is5,5-dimethylol-2-(2,4,6-trimethylphenyl)-1,3-dioxane and/or5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane.
 6. The polyester resinaccording to claim 5, wherein the diol represented by formula (I) is5,5-dimethylol-2-(4-biphenylyl)-1,3-dioxane.
 7. The polyester resinaccording to claim 1, wherein the entire diol unit contains the unitderived from the diol represented by formula (I) in an amount of 1 to 30mol %.
 8. The polyester resin according to claim 1, which exhibits thefollowing properties (1) to (3): (1) a midpoint glass transitiontemperature of 110° C. or higher as measured through the plastictransition temperature measuring method in accordance with JIS K7121;(2) an intrinsic viscosity (IV) of 0.2 to 1.0 dL/g as measured at 25° C.by use of a solvent mixture of phenol and 1,1,2,2-tetrachloroethane(ratio by mass=6:4); and (3) a melt mass flow rate of 10 to 200 g/10 minas measured through the melt mass flow rate test method in accordancewith JIS K7210 at a test temperature of 260° C. and a load of 2.16 kgf.9. An optical lens produced through molding of the polyester resinaccording to claim
 1. 10. The optical lens according to claim 9, whereinwhen the polyester resin is injection-molded into a right-angledisosceles triangular test piece having a thickness of 3 mm in which thelength of each of the two sides forming the right angle is 20 mm, andthe test piece is subjected to annealing for 10 hours at a temperaturelower by 20° C. than the glass transition temperature of the resin, thetest piece exhibits an Abbe number of 20 or less.
 11. The optical lensaccording to claim 9, which is a lens for a camera.
 12. An optical lenssystem comprising the optical lens according to claim 9.